1. Field of the Invention
This invention relates to optical scanners for reading indicia of varying light reflectivity, and in particular to minimizing power usage and improving the aiming of such scanners.
2. Description of the Related Art
Various optical readers and optical scanning systems have been developed heretofore for reading indicia such as bar code symbols appearing on the label or on the surface of an article.
The symbol itself is a coded pattern of indicia comprised of, for example, a series of bars of various widths spaced apart from one another so bound spaces of various widths, the bars and spaces having different light reflecting characteristics. The readers in scanning systems electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumeric characters that are intended to be descriptive of the article or some characteristic thereof. Such characteristics are typically represented in digital form and utilized as an input to a data processing system for applications in point-of-sale processing, inventory control and the like. Scanning systems of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,369,361; 4,387,297; 4,409,470; 4,760,248; 4,896,026, all of which have been assigned to the same assignee as the instant application. As disclosed in the above patents, one embodiment of such scanning systems includes, inter alia, a hand held, portable laser scanning device supported by a user, which is configured to allow the user to aim the scanning head of the device, and more particularly, a light beam, at a targeted symbol to be read.
Such prior art hand held devices generally incorporate a light-receiving module which receives the light that has been reflected from the bar code symbol and determines, from the reflected pattern, the sequences of bars and spaces within the symbol. The unit may also incorporate decoding circuitry to decode the received information and to recover the underlying data (for example the alphanumeric data) which the bar code symbol represents.
It may in some circumstances be disadvantageous for the light generating and emitting module to be housed within the same unit as the light-receiving module and the decoding circuitry. In the first place, locating everything within the main housing requires that the bar code to be read is positioned so that most or at least a substantial proportion of the reflected light returns to the unit along the same path as the emitted light. It might not always be convenient for a user to position the bar code reading and/or the bar code so that the light is reflected back along the same path in that way. Secondly, locating everything within the same unit means that the unit has to be physically rather large and relatively heavy. Users may not find it easy to operate for long periods.
In the field of laser pointers, it is known to provide small hand held units which users can use at conferences, seminars or the like for pointing purposes. The visible spot of the laser beam, when shone onto a screen, indicates to the audience the point of interest, and enables the lecturer to dispense with the traditional physical pointer. Although modern laser pointers are relatively small and compact, they nevertheless still have to be grasped in the hand of the lecturer, which naturally restricts the lecturer""s user of that particular hand. Typically, the laser pointer has to be put down every time the lecturer wishes to do something else, such as to turn over a page in his or her notes, or to operate an overhead projector.
According to a first aspect of the present invention there is provided an optical system for and a method of reading bar code symbols on a target by moving a laser beam directed toward the target in a scan across the symbol during a scan period that commences and ends at opposite scan end-limiting positions, respectively, of the scan. Power usage of the system is minimized by intermittently operating and energizing a light source during the scan period over a duty cycle prior to reading the symbol, to emit the laser beam for a working time period which is less than, and a fraction of, the scan period. The intermittent and cyclical nature of energizing the light source produces multiple images of the light beam on the symbol to visually enhance the aiming of a hand-held scanner at the symbol.
The invention may be carried into practice in a number of ways, and several specific embodiments will now be described, by way of example, with reference to the drawings.